Bioturbation and erosion rates along the soil-hillslope conveyor belt,part 2: Quantification using an analytical solution of the diffusion–advection equation

Particles on soil-mantled hillslopes are subject to downslope transport by erosion processes and vertical mixing by bioturbation. Both are key processes for understanding landscape evolution and soil formation, and affect the functioning of the critical zone. We show here how the depth–age information, derived from feldspar-based single grain post-infrared infrared stimulated luminescence (pIRIR), can be used to simultaneously quantify erosion and bioturbation processes along a hillslope. In this study, we propose, for the first time, an analytical solution for the diffusion–advection equation to calculate the diffusivity constant and erosion–deposition rates. We have fitted this model to age–depth data derived from 15 soil samples from four soil profiles along a catena located under natural grassland in the Santa Clotilde Critical Zone Observatory, in the south of Spain. A global sensitivity analysis was used to assess the relative importance of each model parameter in the output. Finally, the posterior probability density functions were calculated to evaluate the uncertainty in the model parameter estimates. The results show that the diffusivity constant at the surface varies from 11.4 to 81.9 mm² a^-1 for the hilltop and hill-base profile, respectively, and between 7.4 and 64.8 mm² a^-1 at 50 cm depth. The uncertainty in the estimation of the erosion–deposition rates was found to be too high to make a reliable estimate, probably because erosion–deposition processes are much slower than bioturbation processes in this environment. This is confirmed by a global sensitivity analysis that shows how the most important parameters controlling the age–depth structure in this environment are the diffusivity constant and regolith depth. Finally, we have found a good agreement between the soil reworking rates proposed by earlier studies, considering only particle age and depth, and the estimated diffusivity constants. The soil reworking rates are effective rates, corrected for the proportion of particles actually participating in the process. © 2019 John Wiley & Sons, Ltd.     

Luminescence dating of cobbles from Pleistocene fluvial terrace deposits of the Ara River,Japan

Constraining the ages of fluvial terraces is essential to understanding fluvial responses to climate and sea-level changes and estimating uplift/incision. Luminescence dating of sand or silt grains from fluvial terrace deposits in Japan is difficult because sand layers are often absent from gravelly deposits, quartz grains are typically dominated by medium/slow components and/or contaminated by feldspars, and short transport distances and short residence times in riverbeds result in poor bleaching of luminescence signals. Luminescence dating of cobbles may overcome these difficulties, but few studies have applied this technique to fluvial terrace deposits. Here, we examine the utility of luminescence dating applied to three granodiorite cobbles from a late Pleistocene fluvial terrace deposit of the Ara River, Japan. We investigated variations of the infrared stimulated luminescence (IRSL) and post-IR IRSL signals with depth in each cobble. The IRSL and post-IR IRSL signals generally increase with depth, indicating that the cobbles were not completely bleached before deposition. Nonetheless, the IRSL ages of the cobble surfaces (19–17 ka) are consistent with the age of a tephra layer (16–15 ka) at the base of loess deposits overlying the terrace. In contrast, IRSL ages of sand-sized feldspar grains overestimate the depositional age because of incomplete bleaching, whereas silt-sized quartz grains greatly underestimate the depositional age, likely because of the thermal instability of the medium component. Our results demonstrate that luminescence dating of cobbles could provide a better understanding of fluvial systems in which luminescence dating of sand grains is difficult.     

RESIDUAL POST-IR IRSL SIGNALS OF POTASSIUM FELDSPAR FROM MODERN SAG POND DEPOSITS OF CENTRAL ALTYN TAGH FAULT: IMPLICATION FOR DATING YOUNG PALEOSEISMIC EVENTS

The Altyn Tagh Fault(ATF)is one of the most prominent active strike-slip faults in the India-Eurasia collision. Fresh features of surface ruptures, which are attributed to seismic events taking place in the last millennium, are identified at several sites along the Che'erchen River to Qingshui River section on the central part of ATF. Accurate chronology of these earthquake events would help understand the spatial-temporal relationship of the recent earthquakes. However, great difficulties are encountered. The central ATF is located in the arid area, and the vegetation cover is so limited that rare organic materials appropriate for radiocarbon dating can be found in the sediments. Luminescence dating technique may serve as an alternative to directly determine the burial ages of the earthquake related sediments. The optically stimulated luminescence(OSL)signal of quartz, which has been widely employed for luminescence dating, displays unwanted charateristics for accurate dating. Firstly, the quartz OSL signal is not sensitive to irradiation, which leads to low signal-to-noise ratio or even no measurable quartz OSL signal. Secondly, the targeted samples of the last millennium are very young, and the radiation dose received during the burial is expected to be less than 3~4Gy, which futher deteriorates the signal-to-noise ratio of the quartz OSL signal. Therefore, quartz OSL signal is not appropriate for dating the sediments relevant to the recent earthquakes on ATF.
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(D_e)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL₁₇₀ signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the D_e plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL₁₇₀ signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL₁₇₀ D_e values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of D_e distribution of well sorted and stratified sag pond deposits is consistent with the minimum D_e value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum D_e values from the MAM-3 and the FMM. The minimum D_e values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL₁₇₀ age would be overestimated by 200~300a.
The post-IR IRSL₁₇₀ procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed.     

Transport process of sand grains from fluvial to deep marine regions estimated by luminescence of feldspar: example from the Kumano area,central Japan

Using the concept of bleaching in optical dating, a new index of sediment sample bleaching percentage (BLP‐2) was developed and applied to evaluate sand grain transport from riverine to deep‐marine environments. As bleached grains in modern sediments have no optically stimulated luminescence (OSL)/infrared stimulated luminescence (IRSL) signal, bleached and unbleached feldspar grains are distinguished by IRSL intensity. The BLP‐2 distribution of present deposits around the Kumano area, on the Pacific coast of central Japan, suggests that sand grains in surface turbidites obtained from the bottom of the Kumano Trough are of flood/storm origin rather than seismogenic origin. The distribution of BLP‐2 tentatively suggests sand grain erosion–transport–depositional processes; for example, origin and transport agencies of shelf sand, and influence of coastal erosion on the beach deposit. Although the present BLP analysis is not yet supported by a rigorous statistical test, it is useful to distinguish recent deposition and remobilization of sand grains. Furthermore, if the depositional age and the luminescence age of sand grains are accurately estimated, sand grain transport processes of old (late Quaternary) sediments may be estimated by the methodology similar to that of the present study.     

Testing the potential of elevated temperature post-IR IRSL signals for dating Romanian loess

In this study we test the potential of the elevated temperature infrared stimulated luminescence (IRSL) signals for dating Romanian loess. The recently developed post-IR IRSL protocol is applied to Romanian loess using polymineral fine grains extracted from the loess-palaeosol sequence at Mircea Vodă (SE Romania). This approach is aimed at obtaining an additional age control to examine the age discrepancy obtained from previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11 μm and 63–90 μm).Two preheat post-IR IR stimulation temperature combinations were used, 250–225 °C and 325–300 °C, respectively. The signals obtained are documented in terms of dose response curve, laboratory tests and fading. Although both post-IR IRSL signals exhibit small fading rates, dose response characteristics indicate that these rates may be laboratory artefacts. The post-IR IRSL signal stimulated at 300 °C is observed to suffer from dose dependent initial sensitivity changes as both natural and regenerated signals are observed to lie above the saturation level of the dose response curve. Uncorrected age results obtained using both post-IR IRSL signals are in general agreement with previously reported silt-sized quartz OSL ages for samples collected from the uppermost loess unit L1. For older material, the post-IR IRSL signal stimulated at 225 °C is considered to provide reliable age results, in agreement with independent age control available for this sequence.     

Comparison of paired quartz OSL and feldspar post-IR IRSL dose distributions in poorly bleached fluvial sediments from South Africa

A comparative study using quartz optically stimulated luminescence (OSL) and feldspar post-infrared infrared stimulated luminescence (post-IR IRSL) was undertaken on Quaternary fluvial sediments from an unnamed tributary of the Moopetsi River in South Africa. The aim is to assess whether the post-IR IRSL signal can be used to date incompletely bleached sediments. Several post-IR IRSL signals using varying stimulation and preheat temperatures were investigated; of these the post-IR IRSL₂₂₅ signal was deemed most appropriate for dating because it bleached most rapidly. The feldspar post-IR IRSL₂₂₅ equivalent dose (D_e) values from this site are consistently larger than those from quartz OSL, probably due to differences in the bleaching characteristics of the two signals. Additionally, the post-IR IRSL₂₂₅ D_e values within a sample showed less variation in precision than the quartz D_e data, possibly due to greater averaging between grains in the feldspar small aliquots. The agreement between ages based on the OSL and post-IR IRSL₂₂₅ signals was better for younger samples (<20 ka) than for older ones (>50 ka); the cause of this variation is unclear.     

Assessing soil mixing processes and rates using a portable OSL-IRSL reader: Preliminary determinations

Employing a portable luminescence reader in a novel approach for studying soil mantles can help to both better our understanding of and determine the relative importance of the different erosional processes operating on a given landscape. By measuring bulk IRSL signal intensity of unprepared regolith samples as a function of depth, a portable reader has been used to rapidly explore patterns and rates of soil mixing within the actively uplifting San Gabriel Mountains, southern California, USA. Both IRSL and OSL measurements were taken from three different hillslope soil profiles collected within a 100 m radius, as well as a number of bedrock samples. To gauge the rates of grain mixing, bulk IRSL signals are converted to dose values by measuring IRSL growth as a function of dose in a conventional luminescence reader using smaller subsamples from key locations. These data are combined with dose rate determinations based on both in-situ NaI gamma spectrometer measurements and chemical determinations of U, Th and K, in order to convert dose values into “effective age” estimates; these values represent mixed regolith and soil, and not age of sediment deposition. This approach has generated soil turn-over histories much more complex than our simple, signal saturation-with-depth model predicts.     

Luminescence chronology of the upper part of the Stari Slankamen loess sequence (Vojvodina,Serbia)

A thick Middle and Late Pleistocene loess-palaeosol sequence is exposed at the Stari Slankamen section in the Vojvodina region situated in the south-eastern part of the Pannonian basin, Serbia. The profile exposes an about 45 m thick series of loess intercalated by at least eight pedocomplexes. Ten samples were dated by luminescence methods using a modified single aliquot regenerative dose (SAR) protocol for polymineral fine grains and for quartz extracts from the upper part of the Stari Slankamen loess sequence. The infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (OSL) signals from all polymineral samples showed anomalous fading, suggesting that the post-IR OSL signal is still dominated by feldspar OSL. The ages ranging from 4.6 to 193 ka were obtained after fading correction. These ages indicate that the loess unit V-L1L1, the weakly developed soil complex V-L1S1 and the loess unit V-L1L2 were deposited during marine isotope stage (MIS) 2, 3, and 4, respectively, and also indicate that the loess unit V-L2 is of the penultimate glacial age.     

Luminescence dating of Holocene sediment cores from a wave-dominated and mountainous river delta in central Vietnam

Sediments of river deltas provide valuable records of past coastal environments. Optically-stimulated luminescence (OSL) dating has become an alternative to radiocarbon dating for constraining the sediment chronology in large deltas that allow for sufficient sunlight bleaching of sediments during the fluvial transport. However, its applicability to smaller deltas with mountainous riverine systems has not been confirmed yet. To check this, we examine multiple signals from two Holocene sediment cores in the wave-dominated Thu Bon River delta in central Vietnam. Two cores were collected, respectively, 3.9 km and 1.2 km inland from the present shoreline and both show a >-25-m thick succession of coarsening-upward mud to sand deposits. Coarse grains (180–250 μm in diameter) of quartz and K-feldspar, and fine grains (4–11 μm in diameter) of quartz and polymineral were extracted from the upper and lower parts of the cores for multi-grain measurements of quartz OSL, and of feldspar infrared-stimulated luminescence (IRSL) at 50 °C (IR₅₀) and post-IR IRSL at 175 °C (pIRIR₁₇₅) to determine burial ages. In addition, facies analysis and radiocarbon dating were conducted. The landward core consists of transgressive to early regressive estuarine and prodelta facies, which is overlain by a sandy beach-shoreface facies. The seaward core consists of a relatively simple shallowing-upward succession from muddy prodelta facies to sandy beach-shoreface facies. All luminescence ages except for pIRIR₁₇₅ of fine grains are mostly consistent with the radiocarbon ages. Instead, pIRIR₁₇₅ ages of fine grains are significantly overestimated with variable offsets. OSL and IR₅₀ of fine grains provide reasonable age estimates, as these grains were likely well bleached during the transport even along a short and steep mountainous river. Consistent age estimates of all signals from sand indicate that sand was well-bleached in the beach and shoreface owing to the frequent sediment reworking by waves and currents. These results support the hypothesis that luminescence dating is applicable to Holocene wave-dominated deltas and reiterate that comparing different luminescence signals is an effective way to check reliability of the age estimates in environments where the sunlight bleaching is not ensured.     

Small aliquot and single grain IRSL and post-IR IRSL dating of fluvial and alluvial sediments from the Pativilca valley,Peru

Infrared stimulated luminescence (IRSL) and post-IR IRSL are applied to small aliquots and single grains to determine the equivalent dose (D_e) of eleven alluvial and fluvial sediment samples collected in the Pativilca valley, Central Peru at ca. 10°S latitude. Small aliquot D_e distributions are rather symmetric and display over-dispersion values between 15 and 46%. Small aliquot g-values range between 4 and 8% per decade for the IRSL and 1 and 2% per decade for the post-IR IRSL signal. The single grain D_e distributions are highly over-dispersed with some of them skewed to higher doses, implying partial bleaching; this is especially true for the post-IR IRSL. Measurements of a modern analog reveal that residuals due to partial bleaching are present in both the IRSL as well as the post-IR IRSL signal. The g-values of individual grains exhibit a wide range with high individual uncertainties and might contribute significantly to the spread of the single grain D_e values, at least for the IRSL data. Electron Microprobe Analysis performed on single grains reveal that a varying K-content can be excluded as the origin of over-dispersion. Final ages for the different approaches are calculated using the Central Age Model and the Minimum Age Model (MAM). The samples are grouped into well-beached, potentially well-bleached and partially bleached according to the evaluation of the single grain distributions and the agreement of age estimates between methods. The application of the MAM to the single grain data resulted in consistent age estimates for both the fading corrected IRSL and the post-IR IRSL ages, and suggests that both approaches are suitable for dating these samples.     

Luminescence signals from modern sediments in a glaciated bay,NW Svalbard

Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores.Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 °C) the ice-proximal sample showed relatively high doses (∼12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 °C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 °C) doses were overall much higher (∼20–55 Gy), which partly is due to a significant (∼12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 °C) signal.In this Arctic environment it appears that bleaching is limited in the first ∼100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 °C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 °C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin.     

Rock and sediment luminescence dating of an ancient circular stone-walled enclosure at Sønnebøe,northern Scania,Sweden

Dating agricultural artefacts such as field walls and clearance cairns using radiocarbon can be challenging, especially since the association with datable material may be poor. Rock surface burial dating using luminescence offers an alternative. Here we report on the luminescence dating of a medieval circular stone-walled enclosure at Sønnebøe, northern Scania, Sweden, using both buried rocks and sediments. Luminescence burial profiles from IRSL signals measured at 50 °C (IR₅₀) indicated significant prior light exposure in 7 of the 8 samples tested (5 granite, 2 felsic gneiss), in some cases multiple exposure burial cycles were indicated. These rock surfaces had apparently been exposed for sufficient time to allow accurate IRSL ages for the most recent burial event. In contrasts, no useful post-IR IRSL profiles were obtained indicating that this signal was not sufficiently reset to allow accurate determination of the burial dose on any of these rocks. IR₅₀ fading corrections (typically ∼50%) were derived by comparing field saturation with that induced in the laboratory. Quartz extracted from sediments surrounding the rocks gave an average measured to given dose ratio of 1.03 ± 0.01 (n = 90), and these sediment samples were then dated using multigrain aliquots; the corresponding feldspar dose recovery ratio obtained using rock samples was 0.98 ± 0.05 (n = 28). A total of 15 ages were derived; 8 quartz OSL ages from the disturbed coarse grained sediments surrounding the structure, and 7 fading corrected IR₅₀ ages from the surfaces of rocks (2–3 mm chips, ∼1 mm thick) used in the construction of the structure itself. The exposure events preserved by the ring enclosure stones unequivocally show wall building taking place at the site between 800 and 300 years ago.     

A test case for anomalous fading correction in IRSL dating

Infrared-stimulated luminescence (IRSL) dating of feldspars has the potential to date deposits beyond the age range of quartz optical (OSL) dating. Successful application of feldspar IRSL dating is, however, often precluded due to anomalous-fading, the tunnelling of electrons from one defect site to another. In this paper we test procedures proposed for anomalous-fading correction by comparing feldspar IRSL and quartz OSL dating results on a suite of samples from continental deposits from the southeastern Netherlands. We find that even after anomalous-fading correction IRSL ages underestimate the burial age of the deposits and argue that this may be a consequence of a dependency of anomalous fading rate on the dose rate and on the absorbed dose.     

Luminescence chronology of fossiliferous fluvial sediments along the middle Atbara River,Sudan

Fluvial sediments of the middle Atbara River Valley, eastern Sudan, contain abundant vertebrate fossils and stone tools. Previous work described two sedimentary units, the Butana Bridge Synthem (BBS) and the Khashm El Girba Synthem (KGS), with three divisions each (BBS1-3 and KGS1-3, from bottom to top, respectively). ²³⁰Th/U dating on bivalve shells suggested an age of ∼126 and ∼92 ka for the basal KGS2 and basal KGS3, respectively, and mammalian biochronology in combination with magnetostratigraphy suggested an age of late Early to early Middle Pleistocene for the underlying BBS. To establish a detailed chronology of this fluvial sedimentary sequence, we collected 17 luminescence samples from both sides of the Atbara River close to the Butana Bridge. Quartz OSL dating was applied to samples from the upper part of the profile (upper KGS2 and KGS3), but the signal reached saturation within the upper ∼10 m of the sequence. To select a suitable feldspar signal to date older samples beyond the limit of the quartz OSL, a comparison of the quartz OSL, feldspar post-IR IRSL at 225 and 290 °C, and pulsed IRSL signal at 50 °C was conducted for a sample from KGS3. The result showed that only the fading corrected pulsed IRSL yielded an age consistent with the quartz OSL, and the post-IR IRSL signals (both at 225 and 290 °C) overestimated the quartz age significantly. We therefore selected the pulsed IRSL signal to date the older deposits. The luminescence ages indicate that the entire BBS - KGS sequence was deposited between 224 ± 23 ka and <17 ± 1 ka, corresponding to marine isotope stages (MIS) 7–2, significantly revising previous conclusions.     

Testing the potential of using coarse-grain feldspars for post-IR IRSL dating of calcium sulphate-wedge growth in the Atacama Desert

The growth of vertically laminated calcium-sulphate wedges in the Atacama Desert is assumed to be driven by the interaction of moisture supply and salt dynamics in the subsurface. Geochronological data of these wedge laminations is yet sparse but indispensable to resolve wedge-growth phases and episodes of moisture supply and to use these deposits as a palaeoclimate archive in the hyperarid environment. Our pilot study presents a first approach of dating a calcium-sulphate wedge from the Atacama Desert using coarse-grain feldspar luminescence dating. Our results show a widespread and clustered equivalent-dose distribution of two wedge samples from ∼20 Gy up to saturation. Optically stimulated luminescence (OSL) of quartz revealed unsuitable properties for dating wedge deposits. Consequently, we applied post-infrared infrared stimulated luminescence (post-IR IRSL) to coarse-grained feldspars. Since feldspar single-grain measurements yielded a low number of luminescent grains, we used 1 mm aliquots as reliable single-grain proxies for genuine single-grain measurements. Data from energy-dispersive x-ray spectroscopy (EDX) showed that the feldspar single grains have large differences in their internal K content, resulting in an averaged internal K content of 3.9 ± 1.0 % for all luminescent grains. This result was subsequently used for dose rate and age calculations. Our results of equivalent-dose distributions and palaeodoses derived from the minimum age model reveal most recent wedge-growth activities at 10.6 ± 2.2 ka and 7.9 ± 1.8 ka for the two wedge samples.     

Luminescence dating of marine sediments from the Sea of Japan using quartz OSL and polymineral pIRIR signals of fine grains

Luminescence dating has long been used for chronological constraints on marine sediments due to the ubiquitous dating materials (quartz and feldspar grains) and its applicability over a relatively long time range. However, one of the main difficulties in luminescence dating on marine sediments is partial bleaching, which causes age overestimations. Especially, partial bleaching is typically difficult to be detected in the fine grain fraction (FG) of marine sediments. The recently developed feldspar post-IR IRSL (pIRIR) protocol can detect non-fading signals and thus avoid feldspar signal instability. In the current study, fine grains were extracted from a gravity core in the northern Sea of Japan, and the aim is to test the feasibility of using different luminescence signals with various bleaching rates to explore the bleaching conditions of fine grain fraction in marine sediments. The results suggest that the quartz OSL signal and polymineral pIRIR signals at stimulation temperatures of 150 °C and 225 °C (pIRIR₁₅₀ and pIRIR₂₂₅) of FG were well bleached prior to deposition. The OSL ages were used to establish a chronology for this sedimentary core and the resulting age-depth relationship is self-consistent and comparable with radiocarbon dates. We conclude that different luminescence signals with various bleaching rates can be used to test the bleaching conditions of fine grain fraction in marine sediments; and the luminescence dating can be applied to marine sediments with great potential.     

Luminescence dating reveals a rapid response to climate change of fluvial terrace formation along the Ani River,northeastern Japan,during the last glacial period

Fluvial terraces along the middle reaches of many Japanese rivers were formed during the last glacial period as a result of changes in sediment discharge related to cooler temperatures and/or reduced water discharge because of lower precipitation. The influence of climate change on these fluvial terraces is not yet fully understood because most previous studies lacked detailed reconstructions of the chronology of terrace development. This study provides a detailed luminescence chronology of fluvial terrace deposits along the Ani River, northeastern Honshu, Japan, and compares that chronology to paleoclimatic records. Eight samples for luminescence dating were obtained from an outcrop of terrace deposits (∼10 m thick) in the Ani River valley. The fading-corrected infrared stimulated luminescence (IRSL) ages are consistent with the fading-corrected post-IR IRSL ages for some samples, which suggests that fading corrections were effective despite the higher fading rates of the IRSL signal. However, for the other samples, the post-IR IRSL ages are significantly older than the fading-corrected IRSL ages due to incomplete bleaching. The pulsed IRSL signals are close to field saturation for older samples, which might have resulted in a greater variation of the ages. Fading-corrected IRSL ages demonstrate periods of rapid aggradation during 105–90 ka and 75–60 ka. Comparison of terrace development with paleoclimatic records indicates that the two periods of fluvial deposition correspond to decreases in precipitation caused by weakened East Asian summer monsoon precipitation and possibly decreases in temperature. The results of this study show that the Ani River responded rapidly to climate change on a time scale of a few tens of thousands of years during the last glacial period.     

Testing the application of quartz and feldspar luminescence dating to MIS 5 Japanese marine deposits

The applicability of both quartz and feldspar luminescence dating was tested on twenty-five samples from a marine succession now forming a coastal cliff at Oga Peninsula, Honshu Island, Japan. The quartz optically stimulated luminescence (OSL) signal shows thermal instability and linear modulated (LM)-OSL analysis revealed the dominance of a slow component. When compared with independent age control provided by two marker tephras, the quartz OSL ages grossly underestimate the depositional age. In contrast, potassium (K)-rich feldspar is a suitable dosimeter when measured using post-IR infrared stimulated luminescence (IRSL) at 225 °C (pIRIR₂₂₅). Scanning electron microscope (SEM) analyses on the feldspar extracts revealed that the grains are amorphous with small crystalline inclusions; using standard internal dose rate parameters, this would result in a too large dose rate. Dose rates were calculated using the observed grain size of 40 ± 20 μm with an assumed K concentration of 12.5 ± 0.5%. The fading corrected pIRIR₂₂₅ ages agree well with independent age control, and the sediments of the Katanishi Formation were deposited between 82 ± 6 and 170 ± 16 ka. This study demonstrates that pIRIR dating of feldspar is a powerful chronological tool for the dating of sediments of volcanic origin.     

The potential of portable luminescence readers in geomorphological investigations: a review

The development of functional portable optically stimulated luminescence (OSL) readers over the last decade has provided practitioners with the capability to acquire luminescence signals from geological materials relatively rapidly, which allows for expedient preliminary chronostratigraphic insight when working with complex depositional systems of late Quaternary age. Typically, when using the portable OSL reader, infrared (IR) or blue post-IR OSL signals are acquired from bulk unprocessed materials, in contrast to regular luminescence dating, which is usually based on measurements on pure quartz or feldspar mineral separates, or on select silt-sized polymineralic portions. To demonstrate the utility of portable OSL measurements, this paper outlines the basic features of portable OSL readers and their constraints. Subsequently, case studies in which the instrument has been used to elucidate cryptostratigraphic variations in sedimentary sequences for geomorphological applications are reviewed. The studies can generally be grouped into three main categories. The first includes studies where the variation of portable OSL reader luminescence signal intensities with depth are plotted to generate profiles that contextualize sediment stratigraphy. In the second group, portable OSL reader luminescence signal intensities are used to interpret sediment processes that shed light on depositional histories. In the last category, luminescence signals from the portable OSL reader are calibrated to approximate numerical burial ages of depositional units. The paper concludes with a discussion of possible future directions. © 2020 John Wiley & Sons, Ltd.     

Luminescence dating of a gigantic palaeolandslide in the Gobi-Altay mountains, Mongolia

In an attempt to date a palaeolandslide that took place along the Baga Bogd Massif, in Mongolia, the infrared stimulated luminescence (IRSL) method has been applied to lacustrine silty sediments directly overlying the landslide mass. The IRSL age estimates obtained on alkali feldspar grains (>40 μm) and polymineral fine grains (4–11 μm) provide a minimum age for the landslide event. The IRSL ages on alkali feldspars corrected for long-term fading using the protocol of Mejdahl (1988, 1989) suggest that the palaeolandslide occurred at the beginning of the Last Interglacial. These are in good agreement with the ¹⁰Be cosmogenic dates obtained on faulted and abandoned alluvial fans in the Gobi-Altay mountains. This study demonstrates for the first time that the IRSL dating method can successfully be applied for establishing landslide chronologies.